Paragonimus westermani: pathogenesis and clinical features of infection.

PATHOGENESIS: Although the pathogenesis of human infection of P. westermani is not fully elucidated, experimental infections of cats or dogs could explain the early phase of paragonimiasis. As the larvae of P. westermani penetrate the intestinal wall and localize in the peritoneal cavity there appears to be a considerable migration inside the abdominal cavity before they direct toward the chest cavity through the diaphragm. Approximately 20 days following experimental infection with metacercariae by oral route first pathological changes can be detected in the pleural cavity with turbid or haemorrhagic exudation containing also numerous pus cells. Also juvenile parasites are often found in the pleural cavity. The diaphragm is another organ that is heavily affected by penetrating larvae and by surrounding intense inflammatory reactions that develop about 25 days after infection. The worms finally get into the lung parenchyma and induce acute exudative pneumonitis and haemorrhage. They gradually mature and are encysted, thereby producing zones of active inflammation with exudate and of collagenous fibrous tissue. The worms are found usually in pairs. When grown up, these worms are often found inside the bronchial lumen lined with bronchial epithelia of squamous metaplastic character. The cysts consist of the parasite and of dense collagenous connective tissue including various inflammatory cells and eosinophils. CLINICAL FEATURES: The most remarkable clinical feature is cough and blood-tinged sputum. In 1907 paragonimiasis was classified into 4 types: chest paragonimiasis, cerebral paragonimiasis, abdominal paragonimiasis and generalized paragonimiasis. The clinical symptoms of chest paragonimiasis are haemoptysis in some cases, and quite a few patients complain of difficulty in breathing.(ABSTRACT TRUNCATED AT 250 WORDS)